Trying to evaluate disease resistance in pigs without employing sick animals is like testing a wetsuit in the desert: doomed from the start. Of course, finding that happy medium where there is enough disease present to get results, without having more than is necessary, can be tricky. As researchers strive to harness genomics and improve disease resilience and sustainability in Canadian pork production, managing the health status of the Natural Disease Challenge Model is paramount to success.
“To accomplish our goals, we want sufficient disease challenge for testing the hypothesis of resilience while keeping mortality at acceptable levels for animal welfare,” said Dr. John Harding, Professor, Department of Large Animal Clinical Sciences at the University of Saskatchewan. “It took a year or so to achieve that balance, and we maintain it through regular oversight and adjustments where needed.”
A prime example of the process is the routine testing based largely on PRRS.
“We want to ensure that every batch of pigs is PRRSV-negative coming in and that they become PRRSV-positive within four weeks in the challenge nursery,” said Dr. Harding. “We also look at feed intake curves and treatment levels. The important thing is that when PRRSV is infecting pigs, I know the typical response for different treatment rates. At this point, we can almost predict what will happen. If we have batches with less disease challenge, we will take steps to increase it, and vice versa, so that we stay within the standard treatment mortality levels that have been outlined for us by the Animal Protection Committee.”
Part of the challenge with this approach is that scientists are dealing with a new model system and have no recipe for exactly how to proceed, so they must be able to adapt on the fly.
“We have new batches of pigs coming in every three weeks, and we see variations in susceptibility, both within and between batches. There is also seasonal change as disease levels are higher in winter than summer. For a three or four year project, you can’t just set medication rates and types and leave them static. Similar to a commercial barn, things are changing daily as disease levels rise and fall. The only difference here is that we are a bit more careful to maintain the presence of disease pressure to support our research.”
Walking that fine line is not easy, but it’s essential for ensuring the project results will be relevant to producers.
“We are trying to mimic what happens on commercial farms. In the big scheme of things, our disease activity must be similar to that of industry, and that includes both the level of disease challenge and the breadth of disease.”
Though they don’t measure every disease on a regular basis, researchers aim to expose pigs to a variety of diseases in hopes of achieving multi-faceted resilience, with two in particular being the prime focus.
Name that illness
“The two most important diseases are PRRS and mycoplasma pneumonia, so we subject all animals to the former, and most to the latter. Some conditions come and go, but these two continue to plague producers’ farms and pocketbooks.”
By not limiting themselves to one disease, researchers hope to achieve the maximum impact for industry.
“If your only challenge on farm is PRRS, this disease challenge model might not be the most important one to you. On the other hand, if you’re a farmer in the really hog dense regions of Canada, it’s likely you’re seeing PRRS, mycoplasma pneumonia, Strep suis, and other conditions. In that case, you need resilience to multiple diseases, which makes this model, and this project, of particular importance.”
Though some may still embrace the challenge of testing a wetsuit in the desert, testing pigs for disease is far more valuable to producers; not to mention a lot less sweaty.